Nonadrenergic sympathetic neural influences on basal pancreatic hormone secretion

Evidence for peptidergic innervation of the islets of Langerhans is increasing, yet the role of neuropeptides in mediating neurally induced changes of islet function is not clear. To determine if nonadrenergic transmitters make an important contribution to sympathetic neural effects on basal pancreatic hormone secretion, we examined the effect of local sympathetic nerve stimulation (SNS) on the output of immunoreactive insulin (IRI), immunoreactive glucagon (IRG), and somatostatin (SLI) from the duodenal lobe of the pancreas in situ in halothane-anesthetized dogs, under conditions where the actions of the classical transmitter norepinephrine (NE) should be blocked by propranolol (PROP) and yohimbine (YO). In the absence of adrenergic antagonists, SNS rapidly reduced the output of IRI (delta = -1.34 +/- 0.91 mU/min) and SLI (delta = -600 +/- 350 fmol/min) and stimulated that of IRG (delta = +1.39 +/- 0.57 ng/min). In the presence of PROP and YO, SNS induced similar changes of hormone secretion: delta IRI, -1.30 +/- 0.53 mU/min; delta SLI, -480 +/- 180 fmol/min; delta IRG = +1.89 +/- 0.63 ng/min. Because PROP and YO abolished the pancreatic effects of high dose infusions of NE (1 microgram.kg-1.min-1 iv), we suggest that the antagonists produced sufficient, combined adrenergic blockade at the level of the islet, and we conclude that a nonadrenergic neurotransmitter or modulator plays a major role in mediating sympathetic neural effects on basal islet hormone secretion.